1. Field of the Invention
The present invention is broadly concerned with magnetic element temperature sensors, detectors for use with such sensors, closed-loop heating systems making use of the sensors and detectors to wirelessly determine the temperature of an object and to control the object's temperature, and corresponding methods. More particularly, the invention is concerned with temperature sensors made up of at least one magnetically susceptible sensor element, preferably formed of amorphous or nanocrystalline metal, and having a re-magnetization response under the influence of an applied alternating magnetic field which is different below and above at least one set point temperature, such as the Curie temperature of the sensor element. These temperature sensors can be used with correlated detectors for temperature sensing, and as a part of closed-loop heating systems.
2. Description of the Prior Art
A variety of applications for temperature sensors that can be read wirelessly exist in the marketplace. These applications vary from sensing and reporting the internal temperature of livestock to being part of a closed-loop temperature feedback system that allows a magnetic induction heater to precisely control the temperature of insulated food delivery boxes. Many of these applications are disclosed in U.S. Pat. Nos. 5,954,984, 6,232,585, 6,320,169, and 6,953,919.
Many of those applications are currently being served by Radio Frequency Identification (RFID) temperature sensing systems. These RFID temperature sensing systems include an RFID reader and its associated RFID “tag,” whereby the tag has some type of temperature sensor as part of its circuitry.
These prior RFID systems tend to be relatively expensive owing to the cost of the tags, and are unable to operate continuously in excess of 125° C. Moreover, they lack the ability to transmit information in the vicinity of metal or other conducting materials, particularly when the RFID tag is embedded within the conducting material.
Magnetic element markers (or “tags”) are commonly used as part of an electronic article surveillance (EAS) systems or other authentication systems. These markers or tags are passive, typically small, less expensive than RFID tags, can operate at high temperatures, and in some forms, can transmit their information wirelessly to a detector even when embedded within a conductor.
For example, EAS markers or tags made of soft magnetic amorphous alloy ribbons are disclosed in U.S. Pat. No. 4,484,184. These ribbons have a composition consisting essentially of the formula MaNbOcXdYeZf, where M is at least one of iron and cobalt, N is nickel, O is at least one of chromium and molybdenum, X is at least one of boron and phosphorous, Y is silicon, Z is carbon, “a”-“f” are in atom percent, a ranges from about 35-85, b ranges from about 0-45, c ranges from about 0-7, d ranges from about 5-22, e ranges from about 0-15 and f ranges from about 0-2, and the sum of d+e+f ranges from about 15-25. The marker ribbons are capable of producing field perturbations at frequencies which are harmonics of the frequency of an incident alternating magnetic field produced by a field transmitter. A detecting means is arranged to detect magnetic field perturbations at selected tones of the harmonics produced in the vicinity of the interrogation zone by the presence of the marker therewithin. Generation of harmonics by the marker is caused by nonlinear magnetization response of the marker to an incident magnetic field.
There is a need in the art for wireless temperature sensing systems using small, less expensive temperature sensing elements, that can operate continuously at temperatures in excess of 125° C., and that have the ability to transmit information even in the vicinity of metal or other conducting materials. Furthermore, it would be advantageous if such improved temperature sensing elements were able to carry predetermined data relating to the sensor itself or to the object to be temperature sensed, e.g., the identity of the object, object characteristics, or heating instructions. Finally, advantages would be realized if the sensing elements could be used as a part of a closed-loop feedback heating system able to control the output of a heating device and thus control the temperature of an object.